A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphalt shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt strip material, either an organic felt or a glass fiber mat is passed through a coater containing liquid asphalt to form a tacky asphalt coated strip. Subsequently, the hot asphalt strip is passed beneath one or more granule applicators which apply the protective surface granules to portions of the asphalt strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments on the hopper. In the manufacture of colored shingles, two types of granules are employed. Headlap granules are granules of relatively low cost for portions of the shingle which are to be covered up. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof.
Not all of the granules applied to the hot, tacky, asphalt coated strip adhere to the strip, and, typically, the strip material is turned around a slate drum to invert the strip and cause the non-adhered granules to drop off. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper. The backfall granules are eventually recycled and discharged onto the sheet.
To provide a color pattern of pleasing appearance the colored shingles are provided in different colors, usually in the form of a background color and a series of granule deposits of different colors or different shades of the background color. These highlighted series of deposits, referred to as blend drops, are typically made by discharging granules from a series of granule containers. To produce the desired effect, the length and spacing of the blend drops must be accurate. The length and spacing of each blend drop on the sheet is dependent on the relative speed of the sheet and the length of time during which the blend drop granules are discharged. A uniform distribution of blend drop granules on the sheet is also desired. A uniform distribution produces a sharp distinction between the blend drop and the background areas which provides a more pleasing appearance to the shingle. To produce a uniform distribution, a constant flow rate of granules during the discharge is required.
One method of applying granules to the moving sheet involves discharging the granules from feed rolls which are hoppers having a fluted roll. The fluted roll is rotated to discharge the blend drop granules onto the asphalt sheet. The roll is ordinarily driven by a drive motor, the roll being positioned in the drive or non-drive position by means of a brake-clutch mechanism. This mechanical action required to discharge the blend drop granules is burdened with inherent limitations. The duration of granule discharge is too long to produce a short blend drop deposit on a sheet traveling at high machine speeds. Also, the discharge of blend drop granules can not achieve a constant flow rate quickly enough to produce a uniform granule deposit. Consequently, there is a limit to the sharpness of the blend drops on the shingle.
Another method of applying granules to the moving sheet involves discharging granules from an aperture in a nozzle. The granules are fed to the nozzle from a hopper. The discharge of granules from the nozzle is controlled by regulating the flow of granules through the aperture. Generally, the aperture is opened to allow the granules to be discharged from the nozzle and closed to stop the discharge. The flow from the aperture may be aided by gravity, pneumatic pressure or both.
The flow rate of the blend drop granules from the aperture varies while the aperture is opening. The discharge area of the aperture is relatively small when it begins to open. The smaller discharge area provides a reduced flow rate of granules. As the aperture opens the discharge area increases which increases the flow rate until it reaches a maximum flow rate when the aperture is fully open. After this time, the flow rate remains constant until the aperture begins to close. While the aperture is closing, the discharge area decreases which reduces the flow rate until it reaches zero when the aperture is closed. The longer the flow rate variation occurs while the aperture is opening and closing, the less uniform the deposit of granules becomes. In addition, as the speed of the sheet increases the effects of the flow rate variation on the uniformity become more noticeable.
It is desired to provide an improved method for discharging blend drop granules onto the moving sheet to produce a deposit having a uniform distribution of granules.